Abstract: The study investigates supplier encroachment strategies considering product recognition differences and brand spillover effects. It incorporates retailers' external alternatives to establish a multi-stage game model. Using backward induction, the analysis reveals the equilibrium outcomes and optimal strategies for different scenarios, elucidating the impact mechanisms of brand spillover effects on supplier encroachment and retailer switching decisions. Results indicate that when a supplier's product recognition is low, brand spillover strategies may have negative effects, leading to supplier encroachment without relying on retailer brand spillover. When a supplier's product recognition is moderate and the brand spillover effect is within a certain range, the supplier consistently adopts brand spillover strategy for market encroachment. In such cases, retailers do not always resist the supplier's brand spillover strategy and may willing to continue cooperation, achieving a win-win situation. However, when a supplier's product recognition is high, it is always motivated to encroachment, and retailers tend to adopt switching strategies. If the production cost of alternative suppliers is low, the supplier tends to maintain cooperation with retailers. Otherwise, the supplier prefers retailers to adopt switching strategies.